There is a minimum width between lights (depending on vehicle width) and distance from lights to edge of vehicle now, standardised with europe. I suspect if you measure a modern jeep you'll find they have a much wider grill and narrower wings than the ones of old, despite having simular lines.
Most the current regs came out in 1986 which is when E markings are required I think. If your vehicle is older than that you should be able to do what you like if you have sidelights on the wings. Unless your going in for an SVA (can't remember what thats now called) you shouldn't have problems even if its not quite legal, though I'm sure it is. MOT deals with operation safety rather than construction compliance. I know of a couple of late 2As with lights in grill downgrade, never herd them complaining of trouble.
It was export markets that required the move, ours changed due to parts (and styleing) standardisation but I think it happened a year or so later here to use up old stocks. Some places (US?) got lights in wings before the proper recessed wings were avalable so look home made (guess the new regs cought Rover off gard a bit).
